Energetic ions (alpha particles) are by-products of fusion burn in a D-T plasma. It is essential that these ions remain confined and give up their energy to heat the background plasma, thus sustaining the fusion burn. Consequently, the physics of high-energy ions produced by auxiliary heating and by fusion reactions must be understood and controlled in order to progress
to a practical source of power. The CTS development will provide a needed diagnostic tool enabling this progress. Experiments will be carried out on the TEXTOR and ASDEX-Upgrade tokamaks in Germany, which have unique high power gyrotron facilities for providing the high-power millimeter-waves needed for this research.